On-policy distillation fails to improve models on problems they already get wrong

Across five mechanisms and three objectives, on-policy distillation degraded or did not improve accuracy when training was restricted to student failures, with statistical significance.

Academic
Shuo Yang · Zheyu Zhang · Mahito Sugiyama · Gjergji Kasneci

Technical University of Munich · National Institute of Informatics · Munich Center for Machine Learning

Research Digest··2 min read
The authors tested on-policy distillation (OPD) on competition mathematics problems, restricting training to only those problems the student model currently failed.

The authors evaluated five OPD mechanisms (prompt rewriter, soft-prefix encoder, residual-stream offset, per-token cross-attention steering vector, and full fine-tuning) combined with three training objectives (forward KL, reverse KL, direct imitation).

Why this paper

From Technical University of Munich and 2 others

In one line

On-policy distillation degrades accuracy when training is limited to problems a student currently fails, despite decreasing KL divergence; it helps when correct prefixes dominate.

What we could check

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Research Digest

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